function [long_bits] = Extract_process_2(sub_stego)
%UNTITLED3 此处显示有关此函数的摘要
%   此处显示详细说明
long_bits='';
bits='';
dct_stego=blkproc(sub_stego,[2 2],@dct2);%2*2分块DCT2
for x=1:2
  for y=1:2
      extract_block=dct_stego((x-1)*2+1:x*2,(y-1)*2+1:y*2);%拿出每个2*2块
      bits=ext_bit(extract_block);
      long_bits=[long_bits bits];
  end
end
      long_bits=mydouble2char(long_bits);
end

function ext_bit(extract_block)
    if extract_block(1,2)<=extract_block(2,1)
        ext_bit=1;
    else
        ext_bit=0;
    end
end

